well i cant find a specific spec sheet for the transmission fluid brand but in ther perodic maintenance section in service manuals in the 'hydraulic oil, lubricant, and coolant specifications it says this:

"hydraulic and transmission oil (J20A Specification)"
So any brand of transmission oil that meets the J20A spec should work fine.

Find out what type oil has been used in that transmission and check its classification specs, if its J20A rated then use that.
Some customers are fanatics sometimes and only like certain types or brands of fluids, they also may have been told this by another tech previously or called hyster themselves and asked.